It is known in the art to which this invention pertains to provide a nickel-iron electroplating bath which comprises a source of nickel ions provided by nickel sulfate and/or nickel chloride; a source of iron ions preferably in the form of ferrous sulfate; a complexing agent which again may be provided by a number of different compounds; boric acid; and a brightener of which again there are many types known to the art. Experience has indicated, however, that while this general formula offers many advantages over simple electrodeposited nickel-like coatings, primarily by way of corrosion resistance to metallic surfaces, it does upon occasion suffer from at least three disadvantages. The first, by reason of the presence of complexing and brightening agents, there may be an excessive amount of organic breakdown which tends to detract from the appearance of the deposit and may cause degeneration of its physical properties. There may also be present in the bath foreign organic materials which apparently are introduced therein inadvertently from a source such as cutting oils. A second problem with the general bath composition just mentioned is the presence in the bath of zinc and copper impurities. These may come from, among other sources, the workpieces being processed, such as brass parts. A third disadvantage of the general formula stated is that when the nickel-iron alloy has an iron content of about thirty-five percent (35%) or above, there arises rather critical parameters, and bath control is quite difficult.
It has been proposed by the prior art to endeavor to overcome the organic breakdown problem by treating the solution with a material such as activated carbon, however, this is a time-consuming and a relatively expensive procedure. With regard to the problem of the presence of zinc and copper deposits, it is known to use electrolytic purification, that is, to electrolyze the solution for rather extended periods of time at very low current densities. Again, this procedure is relatively time-consuming and costly. When working with nickel-iron alloys with an iron content at or above thirty-five percent (35%) and metallic impurities being present, there has not been found in the prior art literature a completely successful formulation which results in a deposit which possesses overall brightness and ductility, satisfactory plating in the recess areas, and optimum leveling.